John deposits 100 at the end of each year for 20 years into a fund earning an annual effective interest rate of 7%. Mary makes 20 deposits into a fund at the end of each year for 20 years. The first 10 deposits are 100 each, while the last 10 deposits are 100 + X each. The fund earns an annual effective interest rate of 8% during the first 10 years and 6% annual effective interest thereafter. At the end of 20 years, the amount in John's fund equals the amount in Mary's fund. Calculate X